1. Field of the Invention
The present invention relates to a method and an apparatus for determining the position of points arranged on a surface of an article so as to enable accurate positioning of an article in an inspection process or the like.
In the synthetic fiber industry, for example, a spinneret having a nozzle plate with a plurality of holes is utilized for spinning a filament from a liquid-state material. It is important to maintain the dimensions of the nozzle holes to within a certain range so as to enable a stable spinning operation and uniform fiber quality. Therefore, the inspection of holes is a daily job in the spinning factory. Spinnerets are periodically examined and, if the nozzle holes have been damaged, are replaced.
The present invention is suitably utilized in the prior stage of such an inspection for determining the position of each hole on the nozzle plate so that it is brought into alignment with the axis of an inspecting instrument. However, application is not limited to this purpose. It may be utilized for assembly of electronic components on a circuit board, in which leads of the components are automatically inserted into apertures in the circuit board.
2. Description of the Related Art
Usually, inspection of an aperture in an article surface, such as a nozzle hole of a spinneret, is carried out by means of a microscope. In this inspection, each aperture of the article must be sequentially brought in the field of view of the microscope. In an automated inspecting system, the overall image of the article to be inspected is taken by a visual sensor, such as a TV camera, prior to examination of each aperture, for obtaining positional information on the apertures and generating signals for sequentially positioning the apertures to an inspecting point. The image, however, often tends to be distorted due to the tilt of the sensor and/or the article and, further, signal distortion inherent to the instrument, whereby the inaccurate information is provided from the sensor, which, in turn, prevents correct positioning of the aperture within the field of view of the microscope. Moreover, even if the image is not so distorted, another problem occurs when an article has a circular profile. That is, in such the case, it is difficult to position it in a definite angular disposition relative to a center thereof without provision of special positioning means. This means arrangement of the apertures is indefinite relative to the visual sensor at every article.